Two weeks ago, Microsoft begin rollng out Hotmail with a single cluster. Right now, a few million customers have the new Hotmail – less than 1% of our customer base.
"We roll out new software slowly at first in order to give our engineers a chance to study the new software running at scale with real customers. This time, we've made a few minor changes to the way Hotmail works "under the hood" in order to make the rollout go even more smoothly for remaining 99% of our customers. This week, we'll put new Hotmail onto a few additional clusters that've slightly different characteristics (different hardware, different mix of customers), which'll help us learn even more. We expect that we'll make a few other tweaks as we learn.
After that, the release will really pick up speed, and we'll start to put new software on more and more clusters," writes Microsoft.